Electricity is ubiquitous to the modern industrial world. Manufacturing facilities and other industrial facilities require substantial electrical energy. To provide the necessary electrical energy to such facilities, electrical cables are needed. These cables may run from a substation or from electrical generators. But regardless of the source of the electrical energy, modern industrial facilities often involve extensive, and sometimes quite long, runs of large, insulated power supply electrical cables.
The cables used in these settings range greatly in size, varying in diameter from approximately 5 mm to greater than 150 mm. In most utility and industrial power supply cable runs, numerous cables are involved. A common arrangement found in these settings is the trefoil configuration, which includes three cables delivering a three-phase electrical power supply. The trefoil arrangement places two cables side-by-side at the base, with the third cable positioned above the other two, forming a sort of triangular cross-sectional shape. The trefoil arrangement is often used, resulting in groups of three cables run together in this roughly triangular arrangement. Groups of trefoil cables may be run or a mixture of cable arrangements may be involved.
The structures used to physically support these electrical cables take various forms. A common form of cable support structure resembles a ladder, with side rails providing substantial physical strength, and rungs extending from rail-to-rail. In this “ladder-type” structure, the cables are extended over the rungs. The cables may or may not be clamped or otherwise secured to the rungs. Groups of cables are typically secured together.
Different practices and standards have developed in Europe and North America for these types of cable runs. In Europe, electrical cables in these industrial cable runs must be secured to each other (i.e., restraining the cables from separating from each other) and to the cable support structures. To satisfy this requirement, the support structures used in Europe typically include rungs with slots or holes to facilitate the use of bolts for connecting cable clamps or cleats (these terms are used somewhat interchangeably, and the term “clamp” will be used herein to include all cable restraining devices of this type) to the rungs. These clamps, therefore, may be bolted directly to the rungs in many European industrial settings.
In North America, however, there are less explicit standards for securing cables to the cable support structures. Perhaps as a result, the cable support structures found in most industrial settings in North America do not include slots or holes in the rungs. This fact makes it difficult to secure cable restraints to the physical support structures. Adaptors have been developed for this purpose, but there remains a need for a better way to secure cables to each other and to the cable support structures used in North America.
Existing cable clamps also require that the electrical cables be lifted and inserted into the clamp. Perhaps because most clamps were developed to restrain cables to each other, the existing clamps are substantially easier to install when the clamps are not required to be secured to the rungs of a cable support structure. Most of the existing clamps require a two-step assembly. First, the clamp must be secured to the rung, typically using a through-bolt in the European industrial setting. Second, the cables must be lifted into the clamp, so that the clamp may then be fastened around the cables. This process may produce a secure arrangement if the clamp is sufficiently strong, but it requires a physically demanding and time consuming assembly process. These demands and difficulties are particularly challenging when there are multiple heavy cables involved. In some settings, the cables may weigh hundreds or even thousands of pounds.
The development of clamps used in these industrial settings has led to at least two shortcomings in the existing art. First, in all settings, including those where there is a ready means for securing the clamps to the rungs, the assembly process requires lifting and moving very large and heavy electrical cables. Second, in most settings in North America (and many other regions of the world) where the rungs have no slots or holes, there is a need for a better means for securing a clamp to the rung.
Some solutions used for securing cables together create risk of cutting the cable insulation. Metallic bands or straps have been widely used for this purpose. If the cables move over time, these types of bands or straps can cut into the insulation, possibly causing failure. It is, therefore, desirable to use a strong clamp that does not rely upon metallic bands or straps in direct, or close, contact with the cables.
The bands and straps described above use minimal space. Other solutions tend to take the opposite approach. Some clamping structures use large blocks of clamps in what is often identified as a cable bus arrangement. These clamps may work well at restraining cables, but require a large amount of space. In addition, if the cables must be lifted into the clamps, the large cable bus arrangement may require lifting cables several inches, or more, to position the cables within the clamps. This process of lifting the cables into the clamps can be time consuming and quite difficult to accomplish.
To fully appreciate the demands faced by these clamps, it is important to understand the magnitude of the forces that may result in the event of a short circuit. When a short circuit occurs, a very large instantaneous current results. Before a circuit breaker or other device may interrupt this current, the electrical cables through which the current flows will experience enormous physical forces. The magnetic fields generated by these large currents are extremely large and can result in flinging and whipping of the cables. When this happens, the cables experience very large axial, lateral, and torsional forces. The clamps needed to restrain cables under these conditions must be very strong. Thousands of pounds of force may exist in the cables during a short circuit situation.
Given these demands, there is a need for a cable restraining device that is capable of securing cables to each other and to the rung of a physical cable support structure whether the rung has slots or holes or no openings of either type. There is a further need for a restraining device that accomplishes these results without requiring excessive lifting or movement of electrical cables. There is need for a strong restraining device that is easy to install, sufficiently strong to restrain cables in even the most extreme short circuit conditions, and capable of being used with almost all types of physical cable support structures.